1. Field of the Invention
The invention relates to an amplifier, and more particularly to a dual-mode capacitive transimpedance amplifier, and a read-out device incorporating the same.
2. Description of the Related Art
FIG. 1 illustrates a conventional capacitive trans impedance amplifier 1 disclosed in U.S. Pat. No. 6,121,834. The conventional capacitive transimpedance amplifier 1 is used to integrate a detection current, which is generated from a radiation detector in response to light signals, such as infrared signals, for a specified period of time, referred to as the integration time, thereby outputting an output voltage (VOUT) proportional to the detection current. The radiation detector is a photovoltaic diode (D), which is an N-on-P typed detector receiving a reference bias (VCOM) at a cathode thereof. The conventional capacitive transimpedance amplifier 1 includes a transistor (M1), a first capacitor (C1), a second capacitor (C2), a third capacitor (C3), a first switch (SW1), a second switch (SW2), and a third switch (SW3).
The transistor (M1) has a gate coupled to an anode of the photovoltaic diode (D), a drain and a source. The first capacitor (C1) is coupled between the drain and the gate of the transistor (M1). The second capacitor (C2) is coupled between the source of the transistor (M1) and ground. The third capacitor (C3) is coupled between the drain of the transistor (M1) and ground. The conventional capacitive transimpedance amplifier 1 has an open loop gain equal to a ratio of the capacitance of the second capacitor (C2) to the capacitance of the third capacitor (C3). The first capacitor (C1) is charged by the detection current from the photovoltaic diode (D) such that the output voltage (VOUT) proportional to a product of the detection current and the integration time is generated.
The first switch (SW1) has a first end 11 receiving a first voltage (VDD), and a second end 12 coupled to the drain of the transistor (M1), and is controlled to switch between an ON-state, where the first and second ends 11, 12 are connected to each other, and an OFF-state, where the first end 11 disconnects the second end 12. The second switch (SW2) has a first end 13 receiving a reset voltage (VRESET) and a second end 14 coupled to the gate of the transistor (M1) and the anode of the photovoltaic diode (D), and is controlled to switch between an ON-state, where the first and second ends 13, 14 are connected to each other, and an OFF-state, where the first end 13 disconnects the second end 14. The third switch (SW3) has a first end 15 coupled to the drain of the transistor (M1), and a second end 16 for outputting the output voltage (VOUT).
However, the conventional capacitive transimpedance amplifier 1 is only adapted to read out the detection current generated from the N-on-P type detector, but cannot read out a detection current generated from a P-on-N type detector. Therefore, improvements may be made to the above techniques.